Aqueous polyolefin emulsions and method of forming same

ABSTRACT

An aqueous emulsion for use in forming a sizing coating for treating a surface of a substrate. The emulsion comprises at least one polyolefin having a weight average molecular weight greater than 10,000; an acid material selected from the group consisting of saturated fatty acids, unsaturated fatty acids which do not includ any hydroxyl groups and mixtures thereof; at least one base; optionally, an emulsifying agent; and a sufficient amount of water to form an aqueous phase emulsion comprising from about 10-50% of solid materials. The emulsion is formed by combining the polyolefin with the fatty acid at a temperature higher than the melting point of the polyolefin to form a first mixture, adding to the first mixture a sufficient amount of base to neutralize the polyolefin and the fatty acid together with the water and optionally the emulsifying agent to form a second mixture; stirring the second mixture at an elevated pressure and at a temperature above the melting point of the polyolefin and subsequently cooling the mixture to a temperature below the melting point of the polyolefin. The emulsion is particularly useful as a component of a sizing for coating and protecting glass fibers for reinforcing polymeric materials.

This is a continuation of application Ser. No. 07/511,478, filed Apr.18, 1990, now abandoned.

FIELD OF THE INVENTION

This invention relates to aqueous phase emulsions comprising a basehaving at least one grafted polyolefin and a process for forming suchemulsions. The invention also relates to the use of these emulsions as acomponent of a finish composition for use with, for example, glassfibers.

BACKGROUND OF THE INVENTION

Synthetic polymers are frequently combined with glass fibers to obtain acomposite product whose properties, particularly the mechanicalproperties, are better than those available with the use of unreinforcedpolymer material. This is particularly true in the case of polyolefins.

When reinforcing polyolefins with glass fibers, it is known to treat thesurface of the fibers with a finish comprising a polyolefin emulsion inthe aqueous phase. This finish, in addition to protecting the surface ofthe glass fibers, which is one of the standard functions of thistreatment, improves the adherence of the fibers to the material whichthey are to reinforce. To optimize the compatibility between the finishcovering the fibers and the matrix to be reinforced, it also is known touse an emulsion having a polyolefin base of a nature close to that ofthe polyolefins constituting the matrix.

Emulsifying polyolefins is relatively easy as long as their weightaverage molecular weight is less than about 10,000. The polyolefin issimply melted while adding suitable emulsifying agents with stirring. Anemulsion is then obtained by subsequently adding the necessary water.U.S. Pat. No. 3,655,353 to Nalley et al. describes an emulsion with apolypropylene base formed according to the process described above.

It is not as simple, however, to emulsify polyelfins when their weightaverage molecular weight is greater than about 10,000 since, in themolten state, the fluidity of such polyolefins quickly becomesinsufficient to obtain an emulsion. Moreover, isotactic or syndiotacticpolyolefins, which exhibit a strong tendency to crystallize during theircooling, are also difficult to emulsify. Because of this crystallizationtendency, the polyolefins generally selected to be emulsified areatactic or amorphous polyolefins.

Several patents recommend techniques for reducing the problem ofcrystallization. For example, U.S. Pat. No. 4,240,944 to Templediscloses the emulsification of a mixture of an amorphous polypropyleneand an isotactic polypropylene after first melting the mixture of thesetwo polymers. The proportion of isotactic polypropylene in this mixtureis less than or equal to 50%.

To obtain emulsions from isotactic polyolefins of high molecular weight,it also is known to dissolve them with heat in an organic solvent whichis immiscible in water, with subsequent addition of the necessary water.Such a process is described, for example, in French patent No. 2 588263. This process requires, however, the subsequent elimination of thesolvent by extraction or by washing and drying.

SUMMARY OF THE INVENTION

An object of the present invention is thus the formulation of anemulsion comprising a base of grafted polyolefins having a weightaverage molecular weight greater than about 10,000 and the developmentof a process for preparing such an emulsion which overcomes thedifficulties encountered in the prior art processes described above.

The invention has as a further object a process of preparing emulsionsformed with amorphous polyolefins and essentially crystalline (isotacticor syndiotactic) polyolefins which does not employ an organic solvent.

The invention also has as its object the production of a finishcomposition containing the subject emulsion for coating glass fibersintended for use in reinforcing polyolefins.

These objects are attained by forming aqueous emulsions comprising: (1)a mixture containing at least one grafted polyolefin having a weightaverage molecular weight greater than about 10,000 and at least onesaturated fatty acid and/or at least one unsaturated fatty acid whichdoes not contain any hydroxyl groups, (2) at least one base, (3) thenecessary water to obtain from 10 to 50% of solid materials, and,optionally, (4) an emulsifying agent.

The emulsion is obtained by mixing together the at least one graftedpolyolefin and at least one saturated fatty acid and/or unsaturatedfatty acid at a temperature higher than the melting point of the graftedpolyolefin to form a first mixture; then by adding to the first mixturethus formed at least one inorganic or organic base, the water and,optionally, an emulsifying agent to form a second mixture. The materialsare then stirred under pressure at a temperature higher than the meltingpoint of the polyolefin and subsequently cooled to a temperature lowerthan this melting point to form the emulsion.

The process of the invention is particularly useful with graftedpolyolefins whose molecular weight is high and/or whose structure isessentially crystalline.

The intimate mixing of the polyolefin(s) and fatty acid(s) by mechanicalmeans as described herein unexpectedly makes it possible to considerablyreduce the viscosity of the polyolefin component in the molten state.Thus, polyolefins having a weight average molecular weight greater thanabout 30,000 and which exhibit insufficient fluidity for emulsificationin the molten state, can easily be emulsified by the process of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, therefore, mixtures having aviscosity low enough to obtain an aqueous phase emulsion comprise, per100 parts by weight of polyolefin, 10 to 50 parts by weight and,preferably, 15 to 30 parts by weight of fatty acid. When the fatty acidcontent is less than about 10 parts by weight, the polyolefin does notbecome sufficiently fluidized to obtain an emulsion. Additionally, whenthe weight average molecular weight of the polyolefin is high, forexample, greater than about 50,000, a fatty acid content of even 10parts by weight may prove insufficient. For polyolefins having such highmolecular weights, it is preferable to include at least 15 parts byweight of fatty acid.

For the very high molecular weight polyolefins, it may be necessary tointroduce a large quantity of fatty acids. However, in manyapplications, the proportion of polyolefin in the emulsion should remainhigh, and it is therefore desirable that the fatty acid content notexceed 50 parts by weight.

The grafted polyolefins to which the invention applies are polymers ofethylene compounds comprising from 2 to about 6 carbon atoms, such as,for example, polyethylenes, polypropylenes, polybutenes,polyisobutylenes, etc. The preferred polyolefins for use with theinvention are the polyethylenes and homopolymers and copolymers of thepolypropylenes.

The grafted polyolefins used in the invention include, for example,polypropylenes grafted by acids or anhydrides such as maleic, acrylic ormethacrylic acid or their anhydrides, or by oxiranes such as glycidylacrylate or glycidyl methacrylate.

These polyolefins are mixed with saturated fatty acids such as stearic,lauric and myristic acids, or unsaturated fatty acids such as oleic orlinoleic acids. However, all the unsaturated fatty acids are not usablein the invention. It has been observed in particular that ricinoleicacid, comprising a substituted hydroxyl group, does not allow thepolyolefins to become sufficiently fluidized to form the emulsion.

Mixing of the grafted polyolefins and the fatty acids offers theadvantage of fluidizing these polymers without splitting theirmacromolecular chains. This is important if the emulsion to be formedfrom such a mixture is subsequently to be included as part of thecomposition of a finish for glass fibers. Actually, when the material tobe reinforced is a high molecular weight polyolefin, it is desirable toassociate this material with glass fibers having a finish comprising anemulsion of a polyolefin whose macromolecular chain is of similarstructure to that of the polyolefin to be reinforced. This imparts thebest possible mechanical properties to the composite product thusformed.

Another advantage to associating the material to be reinforced withglass fibers having such a sizing is that in such a situation it is notnecessary to eliminate the fatty acid after having fluidized thepolyolefin, in contrast to some additives such as the organic solvents.

In a manner known in the art, the acid functions upon the graftedpolyolefin are neutralized by a base, which can be organic or inorganic.Thus, the base present in the emulsion of the invention may be analkaline or alkaline-earth metal hydroxide, ammonium hydroxide or anamine such as diethylethanolamine or dimethylaminopropanol. Moreover,the base which is selected should be added in an amount sufficient toalso neutralize the acid function of the fatty acid.

Another advantage of the present invention is that the emulsion may beobtained without using an emulsifying agent, which role is played by theneutralized fatty acid. However, in some cases, to obtain a fineemulsion which is stable over time, it is useful to add a separateemulsifying agent in amounts up to 20% by weight of the solid material.The emulsifying agents which may be used in the invention includenonionic compounds, anionic compounds and cationic compounds, which areall well known to one skilled in the art.

The process for producing the aqueous emulsion according to the presentinvention comprises:

a) combining at least one grafted polyolefin with at least one saturatedfatty acid and/or at least one unsaturated fatty acid which does notcontain any hydroxyl groups, at a temperature higher than the meltingpoint of the polyolefin to form a first mixture;

b) adding to the first mixture thus obtained at least one inorganic ororganic base, an amount of water necessary to obtain from 10 to 50% ofsolid materials and, optionally, an emulsifying agent to form a secondmixture; and

c) stirring the second mixture under pressure at a temperature higherthan the melting point of the polyolefin and then cooling the mixture toa temperature lower than this melting point.

Aqueous emulsions of polyolefins, particularly of polypropylenes, arebest suited for surface treatment of a number of substrates. This isparticularly true in the case of emulsions formed according to thepresent invention, which can be used to impregnate or coat fibers,fabrics, films and materials as different as paper, wood, asbestos ormetal. Use of these emulsions makes it possible to render a hydrophobicsurface resistant to chemical products or impermeable to gases. They canalso serve as demolding agents.

One preferred application of the emulsion of the invention is in theformulation of a finish composition which can be deposited on thesurface of glass fibers to reinforce a polyolefin. This finishcomposition comprises, besides the emulsion formed according to theinvention, a number of additional components well known to those skilledin the art. These components include coupling agents, usually silanessuch as gamma-aminopropyltriethoxysilane and, optionally, cationic ornonionic lubricating agents, film-forming agents and antistatic agents.Additional additives may be included within the composition of such afinish depending upon its intended application.

As shown in the following examples, the finish compositions made fromemulsions according to the invention comprise on the order of 2 to 15%by weight of the emulsion. The polyolefin-fatty acid mixtures wereformed in a mixer at a high shearing rate at a temperature on the orderof 170° C. The mixture obtained was subsequently cooled and then ground.

The ground mixture was introduced into a reactor with the variousingredients necessary for emulsifying the polyolefin component. In theexamples provided below, an amount of deionized water necessary toobtain an emulsion at 25% by weight of solid materials was added. Thereactor, having a spherical shape, was equipped at its base with astirrer whose rate of rotation can reach 650 rpm. This reactor also wasequipped with an emulsifier with a high shearing rate able to rotate upto 2,500 rpm.

The rate of stirring and the temperature of the mixture contained in thereactor were gradually increased. When a temperature of about 170° C.was reached, the emulsifier was started for about 45 minutes. As soon asthe emulsifier was stopped, the mixture was quickly cooled withcontinued stirring. The emulsion was then drawn off at about 45° C.

In the following examples of emulsions obtained under these conditions,the molecular weight indicated for the polypropylene used was measuredby the Gel Permeation Chromatography ("GPC") method, which is well knownto one skilled in the art, in a trichlorobenzene solvent, from astandard using polypropylene with a well-defined molecular weight. Thegrain size distribution was measured with a Coulter Counter analyzer,Model TA2, equipped with a 30 micrometer probe.

EXAMPLES

The scope of the invention is further described in connection with thefollowing examples which are set forth for purpose of illustration onlyand which are not to be construed as limiting the scope of the inventionin any manner.

EXAMPLE 1

The polyolefin used was an ethylene-polypropylene isotactic copolymerwith 3% by weight of ethylene, grafted by maleic anhydride. The polymerhad a weight average molecular weight of 66,600. 100 parts by weight ofthis copolymer were mixed with 30 parts by weight of stearic acid.

The fluidized copolymer was introduced into the reactor in the presenceof 12.7 parts by weight of a neutralization amine (i.e.,dimethylaminopropanol), 7.1 parts by weight of a first nonionicemulsifying agent (oxyethylenated octylphenol with 9 moles of ethyleneoxide) and 7.1 parts by weight of a second emulsifying agent which wasalso nonionic (oxyethylenated nonylphenol with 50 moles of ethyleneoxide).

The average particle diameter of the emulsion obtained was 1.8micrometers with 21% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 2

The polyolefin used was the same as that used in example 1. The stearicacid was, however, replaced by lauric acid in the same proportions.

The fluidized polyolefin was neutralized by the addition of 10.2 partsby weight of dimethylamino-2-methyl-2-propanol-1. The same emulsifyingagents, in the same respective proportions, were used as in example 1.

The average diameter of the particles of the emulsion obtained was 2.6micrometers with 55% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 3

The fluidized polyolefin was identical with that used in the precedingexample. The same type and amount of neutralization amine was also used.The two emulsifying agents of examples 1 and 2 were replaced by 14.2parts by weight of oxyethylenated nonylphenol with 100 moles of ethyleneoxide.

The average particle diameter of the emulsion obtained was 2.4micrometers with 49% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 4

The polyolefin used was an ethylene-polypropylene isotactic copolymerwith 2% by weight of ethylene, grafted by maleic anhydride. The weightaverage molecular weight of the polyolefin was 76,900. 100 parts byweight of this copolymer were mixed with 20 parts by weight of stearicacid.

The neutralization amine used was identical with that used in examples 2and 3. It was added in an amount of 13 parts by weight. The emulsifyingagents and amounts used were identical with those of examples 1 and 2.

The average diameter of the particles of the emulsion obtained was 20micrometers with 97% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 5

The various components used were identical to those used in example 4,the only difference being that the amount of stearic acid used was 30parts by weight.

The average diameter of the particles of the emulsion obtained was 3.4micrometers with 70% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 6

The polyolefin was an isotactic homopolymer of polypropylene, grafted bymaleic anhydride, having a weight average molecular weight of 71,200.100 parts by weight of this homopolymer were mixed with 25 parts byweight of stearic acid.

The mixture was neutralized with 16.2 parts by weight of the amine usedin example 2. 6.9 parts by weight of each of the emulsifying agentsadded in example 2 were also included.

The particles of the emulsion obtained exhibited an average diameter of2 micrometers with 38% of the particles measured having a diametergreater than 2.5 micrometers.

EXAMPLE 7

All the ingredients used were identical with those included in example6. Only the proportions of the components of the mixture were different.

10 parts by weight of stearic acid, 7.5 parts by weight of amine and 6parts by weight of each emulsifying agent were combined with 100 partsby weight of homopolymer. The polymer was only able to be partiallyemulsified and the emulsion obtained was very coarse. The remainder ofthe polymer formed a suspension of crystallized irregular grains.

EXAMPLE 8

The ingredients used were identical to those described in example 6.They were added in the following proportions: 30 parts by weight ofstearic acid, 12.7 parts by weight of amine and 7.1 parts by weight ofeach emulsifying agent. These materials were associated with 100 partsby weight of homopolymer.

The emulsion thus obtained was formed from particles whose averagediameter was 2.5 micrometers. 50% of the particles measured exhibited adiameter greater than this value.

EXAMPLE 9

The polyolefin selected was an isotactic homopolymer of polypropylene,grafted by maleic anhydride, whose weight average molecular weight was51,500. 100 parts by weight of this homopolymer were mixed with 20 partsby weight of stearic acid.

The mixture was neutralized with 12.1 parts by weight of the amine usedin example 2. The two emulsifying agents of this example were eachintroduced at a rate of 3 parts by weight.

The average diameter of the particles of the emulsion was 1.7micrometers with 21% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 10

100 parts by weight of the polypropylene used in example 9 were mixedwith 30 parts by weight of stearic acid The mixture was neutralized by7.1 parts by weight of potash. No emulsifying agent was used.

The average diameter of the particles of the emulsion was 5.8micrometers with 80% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 11

The mixture tested was similar to that used in example 10. 100 parts byweight of the polypropylene of example 9 were mixed with 20 parts byweight of stearic acid. The neutralization base was diethylethanolamineintroduced at a rate of 14.4 parts by weight.

As in example 10, the mixture did not contain an emulsifying agent.

The average diameter of the particles of the emulsion was 3.4micrometers with 70% of the particles measured exhibiting a diametergreater than 2.5 micrometers.

EXAMPLE 12

The components of this mixture were identical in nature and inproportions with those of example 9, except for the fatty acid usedwhich, in this case, was ricinoleic acid. 30 parts by weight of thericinoleic acid were mixed with 100 parts by weight of polypropylene.

The polypropylene failed to emulsify despite a fatty acid contentclearly greater than that of the stearic acid used in example 9. Asuspension of irregular grains of crystallized polypropylene wascollected at the output of the reactor.

The aqueous emulsions formed according to the invention may beadvantageously incorporated into finishes to be deposited on the surfaceof glass fibers used to reinforce polyolefins. Moreover, emulsionsproduced according to the invention can be associated without difficultywith the standard components of finish compositions used with glassfibers. These compositions generally comprise, for example, a couplingagent which most often is a silane, preferably an aminosilane; afilm-forming agent selected from polyesters, polyurethanes, acrylics,polyvinyl acetates and epoxy polymers; a lubricating agent, which ispreferably nonionic or cationic; and other optional components such as amoistening agent, an antistatic agent and the like.

The particles of an emulsion formed according to the invention maycomprise from about 2 to 15% by weight of the finish compositiondescribed above. The amount of finish deposited on the glass fibers isbetween about 0.1 and 5% and most preferably between 0.2 and 1.5%.

The finish composition comprising the emulsion according to theinvention can be deposited on the glass fibers by any means known to oneskilled in the art. It can be deposited either at the time of theformation of the glass fibers or at a later stage. The thus treatedglass fibers may be added to the polyolefins in a variety of forms,i.e., as roving or continuous fibers, mats formed from staple fibers orcontinuous fibers, a web, etc. to reinforce these materials.

By way of a comparative example, two finish compositions were prepared.The first finish, which serves as a reference, comprises an emulsionknown as PPRL 3974, marketed by the Proctor Chemical Company. It is apolypropylene emulsion whose weight average molecular weight is lessthan 10,000.

This finish composition comprises the following components, with thecontents being expressed in percentages by weight relative to the totalweight of dry materials:

1% of gamma-aminopropyltriethoxysilane,

6% of the PPRL 3974 emulsion.

The second finish composition comprises the following components,according to the contents expressed as above:

1% of gamma-aminopropyltriethoxysilane,

6% of the emulsion produced according to Example 1.

These finishes were deposited on glass fibers having an average diameterof 13 micrometers. The losses due to ignition of yarns formed fromfibers thus treated are about 0.8%. These yarns were used in the form ofstaple fibers to reinforce, at a rate of 30% by weight of glass, twomaterials with a polyolefin base.

The first material to be reinforced consisted of a polypropylenemarketed by the Appryl Company under the name APPRYL 3030 P.

The second material consisted of the polypropylene used in the firstmaterial to which has been added 1% by weight of an isotacticpolypropylene marketed by the Himont Company under the name HERCOPRIMEG.

The measured values of various mechanical properties of these reinforcedmaterials are given in the Table below. The tensile strength, bendingstresses at rupture and the resistances to the CHARPY and IZOD impactwere measured under conditions respectively defined by the AFNOR NFT57101, AFNOR NFT 51001, AFNOR NFT 51035 and ISO R 180 standards, whichare well known among those of ordinary skill in the art.

                  TABLE                                                           ______________________________________                                                                 Material 2                                                   Material 1       (APPRYL 3030 P +                                             (APPRYL 3030 P)  1% HERCOPRIME G)                                                       Finish             Finish                                                     According          According                                        Reference to the     Reference                                                                             to the                                           Finish    Invention  Finish  Invention                                ______________________________________                                        Tensile 65         76         80      90                                      Stress at                                                                     Rupture                                                                       (Mpa)                                                                         Bending 95        110        120     130                                      Stress at                                                                     Rupture                                                                       (Mpa)                                                                         Unnotched                                                                             15         19         25      33                                      Charpy                                                                        Impact                                                                        (KJ/m.sup.2)                                                                  Notched 90        120        110     140                                      Izod                                                                          Impact                                                                        (J/m)                                                                         ______________________________________                                    

We claim:
 1. A process for forming an aqueous emulsion whichcomprises:a) intimately mixing at least one polyolefin having an initialviscosity value and a weight average molecular weight greater than about10,000 with an acid material selected from the group consisting ofsaturated fatty acids, unsaturated fatty acids and mixtures thereof,wherein said unsaturated fatty acids do not include any hydroxyl groups,at a temperature higher than the melting point of said at least onepolyolefin to form a first mixture wherein the viscosity of said atleast one polyolefin is considerably reduced from said initial value; b)adding to said first mixture a sufficient amount of a base to neutralizesaid at least one polyolefin and said acid material and an amount ofwater sufficient to form a second mixture comprising from about 10 toabout 50% by weight of solid material; c) stirring said second mixtureunder pressure at a temperature above the melting point of saidpolyolefin; and d) cooling said stirred second mixture to a temperaturebelow said melting point to form said aqueous emulsion.
 2. The processof claim 1 which further comprises adding an emulsifying agent to saidsecond mixture to facilitate formation of said emulsion.
 3. The processof claim 1 wherein said first mixture is formed by mixing said at leastone polyolefin and said acid material at a high shearing rate at atemperature of at least about 170° C.
 4. A process for forming anaqueous emulsion which comprises:a) intimately mixing at least oneessentially crystalline pololefin, having an initial viscosity value anda weight average molecular weight greater than about 10,000 with an acidmaterial selected from the group consisting of saturated fatty acids,unsaturated fatty acids and mixtures thereof, wherein said unsaturatedfatty acids do not include any hydroxyl groups, at a temperature higherthan the melting point of said at least one polyolefin to form a firstmixture wherein the viscosity of said at least one polyolefin isconsiderably reduced from said initial value; b) adding to said firstmixture a sufficient amount of a base to neutralize said at least onepolyolefin and said acid material and an amount of water sufficient toform a second mixture comprising from about 10 to about 50% by weight ofsolid material; c) stirring said second mixture under pressure at atemperature above the melting point of said polyolefin, and d) coolingsaid stirred second mixture to a temperature below said melting point toform said aqueous emulsion.
 5. The process of claim 1 which comprisesmixing up to about 100 parts by weight of said polyolefin with said acidmaterial to form said first mixture.
 6. The process of claim 5 whichcomprises mixing from about 10 to about 50 parts by weight of said acidmaterial per 100 parts by weight of said polyolefin to form said firstmixture.
 7. The process of claim 6 which comprises mixing from about 15to about 30 parts by weight of said acid material per 100 parts byweight of said polyolefin to form said first mixture.
 8. The process ofclaim 2 which comprises adding said emulsifying agent to said secondmixture in an amount of up to about 20% by weight of solid material.